Why do we tie the neutral to earth?

[eniacs]

Speaking from ship systems - a 220V supply (or any other voltage supply for that matter) on the ship is floating. There is no tie to ground so the potential difference between any one wire of the supply is only 110V to ground.
Shocks are allways limited to a mild tingle unless of a serious earth fault and shocks are of course limited to only half of the supply voltage unless you manage to get yourself accross both of the live wires...

Why do we not use this system in homes? In the home if your anywhere near anthing metal and manage to touch live, you get the full 220V through you! With a floating system you would only get the 110V tingle and no high currents...

 

[ColJack]

it's to do with the way it's generated over here..

the star point is earthed in a 3 phase supply.

to achieve what you want would mean tying the middle of the generator windings to earth

this would result in having to run 7 wires for translmission rather than 4....

you'd then have 6 phases, with 2 sets of 3 that are 180° out from each other..

 

[ricicle]

Speaking from ship systems....... There is no tie to ground..

You'd have a job

 

[sparkwright]

it's him again.



see him off ban.

 

[eniacs]

Hi Coljac;

Yes the generator windings are down to earth, with a 1 ohm resistor - the only purpose of which is to detect and limit fault currents in the HV side. The LV side of the ship is totally floating - the 3 phase systems are 3 wires only, no neutral.

Yes come on... I've set the trap now bite!

 

[securespark]

Speaking from ship systems....... There is no tie to ground..

You'd have a job

Aw shucks, you beat me to it...

Imagining a very long main earthing conductor running back to port...

 

[securespark]

The LV side of the ship is totally floating

And the Port and Starboard sides too, I would hope...

 

[Aragorn84]

i think Building Site transformers are wired like that in this country?

110v created from two 55v phases that are 180degrees apart.

The yanks also use a split phase system with most domestic appliances running on 110, and 220v available for larger power items like cookers using two 110v phases?

http://en.wikipedia.org/wiki/Split_phase

That goes into it in more detail.

 

[ricicle]

i think Building Site transformers are wired like that in this country?

110v created from two 55v phases that are 180degrees apart

No - one 110v winding that has it's earth centre tapped

 

[Aragorn84]

doesnt that effectively produce two phases that are 180degrees apart?

 

[ricicle]

doesnt that effectively produce two phases that are 180degrees apart?

No, not electrically. It is only one 110V single phase winding, so is not displaced from anything. It's earth is centre tapped so the voltage to either end of the winding is 55V

 

[Spark123]

To the OP
This thread might be of interest:
//www.diynot.com/forums/viewtopic.php?t=195418

 

[Goldberg]

It's earth is centre tapped so the voltage to either end of the winding is 55V

A 110V transformer has an earth?

 

[Spark123]

110v yellow site transformers are Centre Tap Earth hence the need to earth the centre tap so the max voltage to earth seen is 55v from either live,
or are you poking fun as Ricicles senior moment as he should have said winding?

 

[Goldberg]

No, I understand now - the tap winding is centrally neutered.